The present invention relates generally to conveyor belt systems and more particularly, to an apparatus and method for training the idlers on the return side of a conveyor belt to automatically center during operation.
Conveyor belts are used in a variety of industries to transport materials from one place to another. Generally, materials are deposited at one end of a conveyor and are transported to the other end, where they are discharged or otherwise removed from the conveyor belt. FIG. 1 depicts a conventional conveyor belt system 1 which comprises an endless conveyor belt 4 that moves around a tail pulley 2 and a head pulley 3. A load L, provided at load station LS, is delivered onto the delivery side 4A of the pulley 4 just forward of the tail pulley 2. The load L is conveyed on the delivery side 4A in the direction 7A toward the head pulley 3 where off-load station OLS dumps the load L into a receptacle 8 (bin, hopper, etc.). The return side 4B of the conveyor belt 4 moves in the direction 7B back to the tail pulley. To assist the pulleys 2-3, idler roller (“idlers”) are provided underneath each pulley side 4A/4B, namely, delivery side idlers 5 for the delivery side 4A and return side idlers 6 for the return side 4B. Conveyor belts 4 ideally run centered within the conveyor structure. However, certain conditions cause the conveyor belt 4 to move left or right as it travels. This travel is undesirable as it can cause damage to the conveyor belt 4 edge, structure or components. The delivery side idlers 5 and the return side idlers 6 can be used to correct for this undesirable travel.
With particular reference to the delivery side idlers 5, to assist in containing the load material L upon the delivery side 4A of the conveyor belt 4 during transport, the delivery side 4A of the conveyor belt 4 can be formed into a “trough” configuration. FIG. 2 provides an end view looking down the conveyor belt 4 along line 2-2 of FIG. 1 showing one delivery side idler 5 which forms the delivery side 4A of the conveyor belt 4 into a “trough” configuration to assist in containing the load material L. This is typically accomplished via the use of a center roller having angled idlers on each side of the center roller (see U.S. Pat. No. 2,225,276 (Parker)) or by having a Y-shaped support having idlers on each leg of the upper portion of the “Y” (see U.S. Pat. No. 6,405,854 (Cumberlege)). See also U.S. Pat. No. 1,705,558 (Cuddihy); U.S. Pat. No. 1,963,099 (Robins); U.S. Pat. No. 2,561,641 (Thomson); U.S. Pat. No. 2,815,851 (Yoshimura) and U.S. Pat. No. 6,173,830 (Cumberlege, et al.). In addition, due to the uneven loading of the content on the trough-configured conveyor belt, the sides of the conveyor may tend to “creep” along either one of the angled idlers, thereby mis-aligning the conveyor belt. To correct for this “creep” self-aligning tracking assemblies are introduced at predetermined locations along the trough-configured conveyor belts 4. See also Tracker Roller Systems Type R/RG/RC/RRC by Hosch-Fördertechnik GmbH, or the Tapered Self-Aligning Idler Set 2.6.1 by Hebei Xinshan Conveyor Machinery co. Ltd. of Hebei, China.
As for the return side idlers 6, as also shown in FIG. 2, these tend to be single or dual rollers for guiding the return side 4B back to the tail pulley 2. As also mentioned earlier, the return side idlers 6 can be used to correct for the undesirable travel of the conveyor belt 4. As shown in FIG. 3A, a common practice is to angle the return side idlers 6A at their side mounting brackets to force the conveyor belt 4 to move along the center of the conveyor structure (the black arrowhead in FIG. 3A indicates the direction that the idler 6A is directing the belt 4). But this requires continuous adjustment due to the wide range of factors that cause the belt 4 to move.
To avoid having to continually adjust the return side idlers 6A, another solution is to pivotally mount the return side idlers 6B to automatically adjust the angle of the return side idlers 6B and steer the conveyor belt 4 back into central alignment. See FIG. 3B. This automatic adjustment feature of allowing the idler 6B to pivot earns these idlers the term of “training idlers” whereby the training idler has a central pivot, thereby allowing the idler to pivot in the direction needed to steer the belt 4 back to center. Furthermore, in variations of these training idlers, vertical rollers 9 (the tops of which are only shown in FIG. 3B) are used to force the idler 6B to pivot. In particular, the edge of the return side 4B of the conveyor belt 4 contacts the roller 9 and moves that end of the idler 6 in the direction of the conveyor belt 4 movement. This movement of the idler 6B thereby causes the conveyor belt 4 to begin working its way back to the center of the conveyor structure. However, there are several problems with the vertical guide rollers 9:                the conveyor belt 4 must move a significant distance for the edge of the conveyor belt 4 to contact the rollers;        vertical guide rollers are large assemblies and require a large footprint to operate; conventional conveyor systems are designed around having a standard return side idler, and thus cannot support a larger footprint (i.e., the vertical guide rollers); and        contact between the conveyor belt 4 edge and the vertical guide rollers causes damage to the rollers and the conveyor belt edge.        
Another style of return side idlers 6C involve the use of tapered idler ends (see U.S. Pat. No. 5,911,304 (Cumberlege)) which solve some of the problems associated with the vertical guide rollers 9. As shown in FIG. 3C, as the return side 4B of the conveyor belt 4 moves from the center of the idler 6C, the tapered ends 10 of the idler 6C cause the conveyor belt 4 to contact part of the idler 6C with a smaller diameter. As shown in FIG. 3C, the speed differential caused by the difference in diameter (viz., D2<D1) forces the one side of the idler 6C to drag forward, thereby “training” the conveyor belt 4 back to center. However, problems exist with these return side idlers 6C, namely:                as shown in FIG. 3D, some conveyor belts 4 develop a “cupped” profile that causes the conveyor belt sides to “flare” upward which does not permit the belt 4 sides to contact the tapered ends 10 of the idler 6C; the cupped profile typically occurs from the “trough” configuration on the delivery side 4A of the conveyor belt 4;        in certain high tension applications, the conveyor belt 4 maintains a straight profile (see FIG. 3E) but due to the smaller diameter of the tapered ends 10, those ends are also “out of contact” with the return side 4B of the conveyor belt 4.        
Thus, in view of the foregoing, there remains a need for a return side idler that does not suffer from the above-identified problems of conventional return side idlers and thereby maintains sufficient contact with return side of the conveyor belt to “train” the belt, regardless if the return side is cupped or straight, back to center during operation.
All references cited herein are incorporated herein by reference in their entireties.